What is a Black Hole?

Black holes are some of the strangest and most fascinating objects found in outer space. They are objects of extreme density; with such strong gravitational attraction that even light cannot escape from their grasp if it comes near enough.

Astronomers consider a black hole as a stage in the evolution of the star. They are probably formed when a supernova occurs. If a star is ten times more massive than the Sun, no known force can stop the increasing gravity, and it will collapse to a point of infinite density. Before this stage is reached, within a certain radius, light itself becomes trapped and the object becomes invisible, and becomes a black hole.

Albert Einstein first predicted black holes in 1916 with his general theory of relativity. The term "black hole" was coined in 1967 by American astronomer John Wheeler, and the first one was discovered in 1971.

Stellar black holes — small but deadly

When a star burns through the last of its fuel, it may find itself collapsing. For smaller stars, up to about three times the sun's mass, the new core will be a neutron star or a white dwarf. But when a larger star collapses, it continues to fall in on itself to create a stellar black hole.

Black holes formed by the collapse of individual stars are (relatively) small, but incredibly dense. Such an object packs three times or more the mass of the sun into a city-size range. This leads to a crazy amount of gravitational force pulling on objects around it. Black holes consume the dust and gas from the galaxy around them, growing in size.

Supermassive black holes — the birth of giants

Small black holes populate the universe, but their cousins, supermassive black holes, dominate. Supermassive black holes are millions or even billions of times as massive as the sun, but have a radius similar to that of Earth's closest star. Such black holes are thought to lie at the center of pretty much every galaxy, including the Milky Way.

Scientists aren't certain how such large black holes spawn. Once they've formed, they can easily gather mass from the dust and gas around them, material that is plentiful in the center of galaxies, allowing them to grow to enormous sizes.

Supermassive black holes may be the result of hundreds or thousands of tiny black holes that merge together. Large gas clouds could also be responsible, collapsing together and rapidly accreting mass. A third option is the collapse of a stellar cluster, a group of stars all falling together.

Intermediate black holes – stuck in the middle

Scientists once thought black holes came in only small and large sizes, but recent research has revealed the possibility for the existence of midsize, or intermediate, black holes (IMBHs). Such bodies could form when stars in a cluster collide in a chain reaction. Several of these forming in the same region could eventually fall together in the center of a galaxy and create a supermassive black hole.

Interesting facts about black holes

• Black holes do not "suck." Suction is caused by pulling something into a vacuum, which the massive black hole definitely is not. Instead, objects fall into them.

• Miniature black holes may have formed immediately after the Big Bang. Rapidly expanding space may have squeezed some regions into tiny, dense black holes less massive than the sun.

• If a star passes too close to a black hole, it can be torn apart.

• Astronomers estimate there are anywhere from 10 million to a billion stellar black holes, with masses roughly thrice that of the sun, in the Milky Way.

With the invention of invisible radiations like radio waves, urltraviolet, X-rays, gamma rays, etc., locating the invisible black holes has been possible. Black holes are the densest areas in the Universe.